Bug at example from subsection 10.3.1

[Dean Li]

Hi,

In Chapter 10, subsection 10.3.1 "Getting started", the app that dynamically creates input control, would throw an error when combines with isolate().

Here is the code used to create the app:

library(shiny)

ui <- fluidPage(
    textInput("label", "label"),
    selectInput("type", "type", c("slider", "numeric")),
    uiOutput("numeric")
    
)

server <- function(input, output, session) {
    output$numeric <- renderUI({
        value <- isolate(input$dynamic)
        if (input$type == "slider") {
            sliderInput("dynamic", input$label, value = value, min = 0, max = 10)
        } else {
            numericInput("dynamic", input$label, value = value, min = 0, max = 10)
        }
    })

}

shinyApp(ui = ui, server = server)

It throws error at initialization.

At app initialization, input$dynamic is NULL which rise the error. It could be fixed with value=0 (like default) when input$dynamic is NULL:

library(purrr)

server <- function(input, output, session) {
    output$numeric <- renderUI({
        value <- isolate(input$dynamic)
        if (input$type == "slider") {
            sliderInput("dynamic", input$label, value = value %||% 0, min = 0, max = 10)
        } else {
            numericInput("dynamic", input$label, value = value %||% 0, min = 0, max = 10)
        }
    })

}